As is known, the stability of electrical energy supply networks requires that the sum of the power fed in corresponds to the sum of the power drawn. The operators of the energy supply networks therefore control the energy fed in or power drawn in order to maintain this balance. If there is an imbalance, the network frequency changes. If, for example, the energy drawn exceeds the energy fed in, the network frequency decreases, and if the energy fed in exceeds the energy drawn, the network frequency increases.
Since the proportion of decentrally generated energy in Germany is continually increasing, the number of feeders that the grid operator can access directly in order to control their fed-in power is decreasing. Therefore, it is a normative requirement for many decentralized energy producers that they independently control the fed-in power depending on network parameters, in particular the network frequency.
Document EP 2875560 A1 further proposes that consumers also determine the network frequency at their network connection point and compare it with a base value. As a result of the comparison, the consumers control the draw of electrical energy from the energy supply network and thus independently contribute to achieving the balance.
Since the network frequency must be the same within the entire connected energy supply network, this control method can only help to maintain a balance within the entire network. Regionally, there may therefore be a significant imbalance between infeed and consumption of electrical power, which must be compensated for by transmission of electrical power between the regions. Since the capacity of transmission lines between remote sections of the energy supply network is limited, it may happen that these transmission lines are overloaded even though there is a balance between infeed and consumption within the entire network. This is the case if, for example, in the north of Germany a lot of energy is fed into the network without an adequate consumption being realized there and in the south of Germany a lot of energy is drawn from the network without an adequate infeed being realized there.
It is therefore desirable to provide control mechanisms for the infeed and drawing of power into or from an energy supply network that are suitable for ensuring the balance between the infeed and drawing at the regional level as well so that an increase in capacities in transmission lines between remote network regions becomes unnecessary.
The voltage at this point is an insufficient or less suitable indicator because medium-voltage and high-voltage transformers are often equipped with control devices that change the transformation ratio in operation in order to stabilize the local voltage. Because of such voltage control interventions, it is not reliably possible to derive an energy flow direction from the instantaneous voltage.